Fire control system



Oct. 9, 1951 .1. E. REIERSON FIRE CONTROL SYSTEM 5 Sheets-Sheet 1 Filed Nov. 8, 1946 D glwvc/n'fov :Iuhn- E- Reierusun MWMMMW XVZM,

1951 J. E. REIERSON 2,570,276

FIRE CONTROL SYSTEM Filed Nov. s, 1946 s Sheets-Sheet 2 a 02'. B 70a.

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Oct. 9, 1951 J. E. REIERSON FIRE CONTROL SYSTEM Filed NOV. 8, 1946 5 Sheets-Sheet 5 gwucm/lm John E-REiEILSDIL J. E. REIERSON FIRE CONTROL SYSTEM Oct. 9, 1951 5 Sheets-Sheet 4 Filed Nov. 8, 1946 1951 J. E. REIERSON FIRE CONTROL SYSTEM 5 Sheets-Sheet 5 Filed Nov. 8, 1946 MUMM W014 Patented Oct. 9, 1951 UNITED STATES ATENT OFFICE (Granted under the act of March 3, 1883, as amended April 30, 1928; 3'70 0. G. 757) 7 Claims.

The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to a fire-control system adapted for use with any type of artillery, but particularly valuable in connection with guns intended for firing upon moving targets such as aerial. marine, or terrestrial vehicles.

With present systems, it is customary to follow a moving target with one or more sighting devices and to control the gun or guns to move substantially as a unit with the sightmg devices, while simultaneously determining and maintaining an angular relation between the line of sight and gun bore, e. g. the lead angle, based upon instantaneous values Of range, elevation. speed and course of the target.

The accuracy of fire obviously depends upon the accuracy with which the foregoing values are determined and combined. However, the actual range of the point at which the projectile and the target must intersect if a hit is to be efiected, is almost never the same as the instantaneous range, but is the instantaneous range plus or minus a component of movement of the target during the time of flight of the projectile. This component varies with the speed, altitude and course of the target relatively to the gun station and, particularly in the case of fast-moving aerial vehicles, may be sufiicient to seriously afiect the accuracy of fire. Furthermore, it is necessary to assume with such systems that the target will maintain its course and speed constant during the interval between firing the gun and impact.

With the method embraced in my invention, the instantaneous course and speed of the target are accurately determined and physically represented to scale. A fixed point is selected that lies upon said course or path of movement of the craft, the range and elevation of this point from the gun station are determined, and the correct lead angle for this fixed range, speed and course of the target, are computed. The gun is aimed so that its trajectory passes through, or includes, the pre-selected point. while a line, such as a sight line, is established extending from the gun station to and intersecting the predetermined course while making the predetermined lead angle with a line extending between the gun position, and the fixed point. The gun is fired when the target is observed in or along the line of sight. Allowance may be made if desired, for human time lag or other corrections of a more or less fixed nature, that may be involved.

By my method all factors used in calculating the lead angle are definite. This is especially true of the range by reason of the fact that the desired point of impact is selected in advance and, hence, its range is known before the gun is fired and the lead can be determined with a high degree of accuracy.

It is therefore, one object of my invention to provide a method of firing against aerial targets that is rapid, highly accurate, and that will in crease substantially the percentage of hits now considered satisfactory.

Another object is to provide apparatus for carrying out the foregoing method wherein the target path, speed and range are plotted to scale and wherein the lead angles and fuze settings are computed in a simple and facile manner.

Another object is to provide a train-angle precomputed chart which will enable the train-angle for a selected firing point lying on the instantaneous path of the target to be quickly determined and transmitted to the guns.

A still further object is the provision of a gun elevation computing chart which will enable the total elevation angle for the firing point selected, to be rapidly determined and transmitted or applied to the gun or guns.

Another object is to provide a system of integrated and interconnected elements that automatically coact to first, determine the angular values for laying the gun on a selected point on and along the extended target path, and secondly, to determine the horizontal and vertical lead angles or the slant plane lead angle, which, added to the angular values used for laying the gun, will determine the correct angular relation between the gun and line of sight to the target so that a hit will be efiected when the target is observed to be in line of sight.

A further object is to provide a fire control system that eliminates the errors common with director firing where a target must be continu ously followed by two or more sighting instruments operated under manual control.

A further object is to provide a system wherein a definite point is located in advance of and lying upon the extended target course and wherein the gun is trained and elevated so that its trajectory intersects or includes such point, while the sight is directed upon a second aiming point lying upon such course, the spatial relation of the two points being such that the target may be hit by firing the gun when the target appears in or along the line of sight from the gun to said second or aiming point.

A still further object is to provide a system of observing stations and interconnected plotting mechanism by means of which the target course, speed and range, may be quickly and accurately determined.

Another object is to provide a gun fire control system wherein the angles of train and elevation of the gun may be automatically introduced as soon as the firing point has been selected.

A still further object is to provide a gun fire control system wherein a, number of computers are automatically adjusted by the plotter, in accordance with the target course determined thereby relatively to a fixed base line.

Yet another object is to provide a fire control system wherein a gun train angle computer effects control of an elevation angle computer.

Other objects and advantages of my invention will become apparent as the description proceeds.

In the drawings:

Figure l is a perspective schematic View of the general geometrical principles involved in my invention and showing the positions of the target, gun, observing stations, base lines, and target plane, together with explanatory lines between several of the points,

Figure 2 is a plan view of a plotting board on which are represented to scale the horizontal projections of the principal points and lines of Figure 1,

Figure 3 is a plan view showing the general arrangement of the gun, observing stations, plotter and computers, as well as the projection uponra horizontal plane through the gun position of an assumed target course.

Figure 4 is a perspective view of one of the sighting and transmitting units used at each of the observing stations, a part of the sight standard being broken away for clarity of illustration,

Figure 5 is an enlarged side elevation of the instrument shown at Figure 4,

' Figure 6 is a detail View showing means for locking in adjusted position the azimuth plate,

of the sighting instrument,

Figure 7 is a plan view of one form of a target course and'speed plotter for use as an integral part of the system of my invention,

Figure 8 is a section taken upon the line 88, Figure '7, with the target speed scale rotated into parallelism with the diametral slot in the plotting board, and showing the slidable mounting for the speed scale and its associated transmitter, I

Figure 9 is a detail sectional view taken upon the line 99, Figure 7, and showing the detail of the pivotal mounting of the arm of the plotter used to determine the minimum horizontal range of the target plane and the central aiming point,

Figure 10 is a central vertical section through the instrument for computing the angle of gun train for the selected aiming point,

Figure 11 is a perspective view showing the detachable connection between radial arm and its supporting shaft,

Figure 12 is a view of a gun train angle computing chart for use with the instrument of Figure 10,

Figure 13 is a perspective view of an instrument for computing the angle of site for the selected aiming point.

. Figure 14 is a sectional view of the instrument of Figure 13 taken substantially upon the line which my invention effects a solution.

IA-H of Figure 13, with sight, bail and scale elevated to Figure 15 is an elevation of a superelevation computer constructed for use with the instrument of Figures 13 and 14,

Figure 16 is a view of suitable scale graduations, based upon a pre-selected time interval between observations, for directly reading the target speed in connection with the computing instrument of Figure '7,

Figure 17 is a detail view of a portion of the instrument of Figures 13 and 14, taken upon a plane indicated by the line ||l1-, Figure 14;

Theory of operation Figure 1 shows the general problem involved.

in firing at a moving target and the manner in Let G represent the gun position and OI and 02, two observing stations, located at points substantially in the same horizontal plane with the gun. A base line B is determined by the gun position and station OI. A second or auxiliary base line B is determined by a line through station 02 parallel to line B. A sighting device, or radar finder, is located at each of the observing stations and each device is mounted for pivotal movement about vertical and horizontal axes in the manner of a surveying transit, for example, so that each device may be continuously trained upon a target T. This target is represented as moving along a line L in a direction indicated by the arrows and at a constant altitude H, above the horizontal plane through the gun.

A plotting board C, Figure 2, is-located -at any convenient position and has indicated'thereon points representing to a selected scale, the true relative positions of the observing stations Ol, 02 and gun position G together with base lines 13 and B. If the target is continuously sighted and the angles (.11 and ,81 made by-the horizontal projections of the lines of sight from points OI and O2 to the target at any point such as T3, with respective base lines B and B, are noted and plotted on board 0 a first point T3 on board C is determined. Any second point such as T5 on the target path is determined in a similar manner by a second observation determining the horizontal angles a2 and B2. This observation is made a known time interval subsequent to the first observation. A line D connecting points T3 and T5 on board C then enables measurement of the target course relatively to base line B, while the distance between the points, measured on board C, in connection with the aforesaid time interval, enables the ground speed'of the'target to be computed.

The vertical plane through the target path, which path is determined by points T3 and T5, is called thetarget plane and is identified as P, Figure 1, and a perpendicular E dropped from G to this plane represents the minimum horizontal range of the target. A vertical plane through line E intersects the target course at point T5 and this point is the control or central one of a number of firing points TI, T2, T9, equally spaced along the target course. It will be understood that the initial points of observation of the target are selected more or less at random and were taken as the points T3 and T5 merely to avoid a confusing number of lines upon Fig.- ures l and 2. Indeed, the target. plane may be determined before the target reaches, Tl so that any of the points TI to T9 may be selected as the point at which the target .will be .hit. It isv important, too, to note that the central firing point T is determined solely by the vertical plane through line E and that the remaining firing points are determined solely by point T5 and the selected equal intervals between them. This interval and the number of firing points selected are chosen to have the most advantageous number dictated by experience. While nine firing points are shown, this is for the purpose of illustration only, as a larger or smaller number may be used when desired without in any way altering the principles upon which the invention is based.

Having thus determined the target path L on board C and the point T5 thereof, the other firing points may be located along said path in any convenient manner, as by the application of a scale having the points spaced therealong in accordance with the actual selected interval between firing points and the scale of the plot on board C. The battery commander will then select a firing point in advance of the actual target position. The point selected will be based upon experience and tactical consideration such as the most efiective range of the gun, speed and type of target craft, time necessary to plot and compute the necessary values, and the apparent objective of the target.

The elevation of the target may be ascertained by a separate height finder such as the Armys type M2, or merely by laying oil at point OI, Figure 2, for example, a line taking the same angle with line OIT3 that the line of sight from Oi made with the horizontal. The intercept of the two lines through T3, perpendicular to line Ol-T3, will then represent to scale the target altitude or distance H, Figure 1. However, it is immaterial for the purpose of my invention, how the altitude is ascertained, and any of the wellknown instruments or triangulation procedures for efiecting this purpose, may be utilized.

Assuming that the altitude is known and that point T1 is selected as the one at which the target will be engaged, the problem then resolves into two parts, (1) to lay the gun so that its trajectory will pass through or intersect the point T1 and (2) to establish a line of sight angularly related to the gun and intersecting the target path L so that, when the target appears in or along the line of sight, the gun is fired and the target and projectile meet at T1.

Taking up first the problem involved in laying of the gun, the horizontal angle or angle of train relatively to base line B, might be scaled directly from board C and, since the horizontal range from gun position G to point T1 can be scaled off, while the altitude H is known, the angles of elevation and superelevation might be taken from firing tables or charts. These angles are indicated at 9 and t, respectively, Figure the line GF being the actual direction of the gun bore at the time of firing.

The velocity of the target having been determined, as well as the range to point T1 and the time of flight of the projectile to such point, the distance traveled by the target during the time of flight of the projectile may be readily computed. This distance, laid off along line D, Figure 2, in the direction of the target will locate the sighting point at which the target should be observed when the gun is fired, in order to eifect a hit. Suppose that A, Figure 1, represents a point so determined for any particular engagement. The angle w, Figure 1, between the lines from the gun to T1 and A, is the slant plane lead angle and its projection upon the horizontal plane is indicated by 6, Figure 2.

The correct angle of train of the gun will be the angle p, Figure 1-, which may be obtained from board C, Figure 2. The correct elevation angle is the angle 0+, Figure 1, which may be determined as previously explained. The correct lead angle for the sight relatively to the gun may be introduced merely by elevating it through the angle 0 and turning it about a vertical axis relatively to the vertical plane through the gun, through the angle 5. The gun is then fired when the target is observed on the cross wires of the telescope or radar screen. By reducing the time necessary to determine the values mentioned in the foregoing explanation, firing points may be continuously selected and bursts fired at the instant the target is observed along the line of sight. Therefore it is highly desirable that the time consumed in computing and plotting the points and applying the computed angular values to the gun and sights, be reduced to the lowest possible value. It is the purpose of the apparatus hereinafter disclosed, to reduce the computing and plotting times to a minimum.

General construction and arrangement At Figure 3 I have shown schematically one system with which my method may be practised. In this figure, OI, O2 and G represent the observing stations and gun, as previously explained, whose relative positions are accurately known. T represents the instantaneous position of the target and E the minimum horizontal range of the target path extended in advance of the target.

Sighting instruments 1B and 70a which may be of the type shown at Figure 4, are located at stations Oi and 02. One of these will be subsequently described in detail. Sufiice it to say for the present, that each sighting device is universally mounted as by pivotal movement about vertical and horizontal axes, and that the component angular movement of the sight about the Vertical axis is transmitted by any suitable and well-known mechanism, such as a Selsyn or Autosyn transmitter to respective repeaters located at a plotting station, preferably near the uns.

At the plotting station there is provided a plotting or computing instrument H whereon are positioned a pair of arms each pivoted upon a respective axis normal to the plotting surface or area. These axes are so positioned upon the plotting area of the instrument that they represent, to the reduced scale of the instrument, the actual relative positions of the gun and observing stations 0! and 02. Preferably, each arm is directly connected to a Selsyn or Autosyn repeater, each controlled by a corresponding transmitter, so that each arm continuously bears the same angular relation to a predetermined base line on the plotting board, that the horizontal projection of the line of sight bears to the corresponding actual base line. This base line, as previously noted, may conveniently be taken as a line connecting stations Oi and G. By this mechanism the horizontal projection of the triangle OI, T, 02, may be simulated to scale and the position of the horizontal projection of the target continuously determined relative to the gun G. Thus, assuming that the target is travelling in a horizontal path, a line connecting two points determining the instantaneous positions of the target at a known time interval apart,

will be proportional to the distance covered by the target during said interval, so that the speed thereof may be readily determined. Indeed by graduating a scale based upon a predetermined time interval. and scale of the plotting board, the 'velocity may be read directly therefrom. Such a scale is shown at Figure 16.

Thus the course of the target relatively to the predetermined base line, as well as its speed, can be. readily determined. The course thus determined, also determines the target plane and the length of the perpendicular to this course, extended if necessary from point G, represents to scale the distance E, as explained in connection with Figure 2. 1

By mechanism incorporated into the plottin board or computer, and subsequently described, I propose to transmit the angle that the normal to said course line makes with the base line, directly to one or more computers for the train angle for the particular firing point selected, whereby this value is automatically introduced.

The train angle computer is shown in detail at Figure 10, while the elevation angle computer is shown at Figures 13 and 14. These are intended either to control the gun directly to move the same in train and elevation through known servomotor and follow-ups, or merely to afford indications at the gun. In the latter case, the gun may be properly trained and elevated by a manually-operated follow-the-pointer-system. The gun has a sight mounted thereon. This sight may be connected for movement as a unit with the gun and, when desired, disconnected therefrom so as to be unaffected by adjustment of the gun for superelevation. The sight is also angularly adjustable relatively to the gun about an axis normal to the slant plane of the target, whereby to set off the angle of lead relatively to the gun in said plane. This movement of the sight relatively to the gun may also be effected automatically or by hand.

For simplicity and clarity of illustration, only one gun will be shown and described. However, it will be understood that a battery of guns may be controlled by one installation merely by providing a plurality of repeaters. The gun having been thus aimed and the sight thereof having been set relatively to the gun by the computed lead angle, is fired at the instant the target appears centered in the field of view of the gun sight. The time interval between the initial sighting and firing will be a few seconds only so that a single target may be fired upon as it passes through successive aiming points. It will be understood that the term sight or sights is intended to include any apparatus by which the instantaneous position of a line from the gun and observation stations to the target may be determined. The term includes direct sighting, as well as radar equipment and sound locators.

The sights At Figures 4 and 5, I have shown a sight gen erally designated at 70, that may be used at the stations such as O l and 02. The sight proper comprises a prism telescope ll of well known construction, having a prism casing I la carrying an ocular ill) at one side, and an objective He at the other side and at a fixed angle to the ocular axis. A segment of circular rack 12 is secured to casing Ha. ihis casing also carries aligned pivot pins 13 and M at opposite sides thereof. The axis of these pins coincides with the axis of rack 12. A frame 15 has upstanding arms 15c and 1512 each of which has at its top, a bearing portion in which the pins 13 and 14 are respectively journaled and held in position by bearing caps 16 and 11. A pinion 18 is fixed to a shaft 19 journaled in frame 15 and meshes with an idler 9| also journaled in frame 15. Idler gear 9| meshes with rack or segment 12. A handwheel BI] is attached to shaft 19 and it will be noted that as this handwheel is turned, the sighting device is moved about the normally horizontal axis defined by pins 13 and M, the directions of rotation of the line of sight and handwheel being the same.

Frame 15 has a shaft or pintle 150 secured thereto or formed integrally therewith which is journaled within the frame 8|, in turn, carrying the electric telemetric transmitter whose casing is indicated at 82. As shown, the top of frame 8| is formed as a circular disk or plate graduated in degrees of azimuth. This disk is rotatably supported by a flanged ring 83 that, in turn is mounted upon a tripod head 84, by means of the leveling screws 85, 86, etc. Transmitter 82 may be a conventional Selsyn" or Autosyn having its armature directly connected, or geared through step-up gearing, to shaft 150. At 81 I have indicated an electrical cable by which the field coils of the transmitter are connected to the corresponding coils of the repeater and the armature energized in the manner well known in the art.

A pointer 88 is secured to shaft 150 and has its tip moving over and cooperating with, the scale upon frame 8|. This pointer is preferably secured to shaft 150 so that its radius lies in the plane determined by the optical axes of sight II. It is provided with a handle 88a for manual operation of the sight about the axis of shaft 150. A thumb screw 89 and clamp 90, Figure 6, are effective to lock frame 8| in any desired position of rotational adjustment within ring 83.

The operation of these sights will now be clear. Each is set up over a point whose coordinates with respect to the gun, are known. Ring 83 is leveled by manipulation of screws 85, 86, etc., after which screw 89 is loosened and frame BI is rotated with respect to ring 83 until the 0-180 diameter thereof is parallel with the predetermined base line that as previously explained, may conveniently be a line connecting stations OI and G. Screw 89 is then tightened to lock frame 8| in adjusted position and connections are made over cable 81 to a corresponding repeater at the plotting instrument. The operator grasps handle 88a with one hand and handwheel with the other and, while looking into ocular N b, so adjusts the knobs as to maintain the selected target in view. Thereby the instantaneous angular position relatively to the base-line of the horizontal projection of the line of sight, from that station to the target, is continuously transmitted to the plotting station. As previously mentioned, one of these sighting instruments will be located at each sighting station and one or more stand-by instruments may be located at auxiliary known sighting positions for use in event one of the regular sights is put out of operation during combat or in event the tactical situation renders it advisable to substitute an auxiliary station in place of one of the stations OI or 02.

The plotting instrument The plotting instrument I is shown at Figures 7, 8 and 9, and may comprise a flat support or base 2|, mounted upon a suitable tripod and leveling head or other leveling support, not shown. A base line 22 is formed upon base 2| and a bracket 23 is secured thereto, Figure 9, centrally of line 22. An arm 24 is pivoted to bracket 23 upon an axis that intersects base line 22 at the central or control point thereof. This point represents the gun position G. Arm 24 is graduated to the scale of the instrument and carries numerals, not shown, indicating in feet or yards, the radial distance from point G to any point upon the board within a semi-circular mil scale 26 formed concentric of point G. Scale 26 may be graduated at one side in any convenient steps, such as IOU-mil units from at its left terminus, clockwise to 3200 mils, and at the other side from 3200 mils, counter-clockwise to 6400 mils, as clearly shown upon the figure.

An arm 29 is pivoted at a point on line 22 that is removed from point G, a distance equal, to the scale of the instrument, to the distance between the actual stations OE and G. A protractor scale 28 is secured to base 2| with its center coincident with the pivot of arm 29 and its O-180 line coincident with line 22, whereby the angular position of arm 29 relatively to line 22, may be read. Likewise, a second arm 36 is pivoted at a point upon base 2! that represents sighting station 02; and it will be noted that the point is shown as offset from line 22, thus emphasizing the fact that the positions 01, G and 02 are not required to be aligned but, within practicable limits, may have any spatial relation. However, the distance that point 02 is located from G and its offset from base line 22, are to the scale of the instrument, equal to the corresponding distances of the actual observation point 02. Thus the board simulates to scale the tactical set-up of the apparatus.

Arm 29 is fixed to the armature shaft of a repeater motor 22 mounted on and beneath the base. Likewise arm 36 is fixed to the armature shaft of a repeater motor l3 also mounted on and beneath the base. Preferably the casing of each of said repeaters is rotatably mounted about the axis of its arm relatively to base 21, in order to facilitate initial adjustment of the instrument to make sure that each arm 29 or 30, is synchronized with its corresponding sight.

Base 2| is provided with a slot l4 extending from point G, normal to line 22. A slide l6, Figure 8, is mounted for guided translation along this slot and the casing of a transmitter 18 is secured to said slide. The armature shaft is of said transmitter passes through an opening in slide is and at its projecting end carries a channeled guide element 25 within which a scale 3! fits and is adapted to slide. Because of the slidable pivotal mounting thus afforded scale 3! may be moved into alignment with any two points located upon the plot-ting surface of base 2 i, while the angle of rotation thereof is effective upon transmitter 5'8 so that the rotation of the latter may be used to transmit said angle of rotation toany desired points, for a. purpose subsequently explained.

In this manner, as repeaters l2 and i3 are controlled from their respective sighting stations and thus act to continuously control the angular positions of arms. 29' and 30, the intersection of the radial edges of these arms will at all times represent the instantaneous position of the target in a horizontal plane. Thus, if these positions are noted at a predetermined time interval apart, the horizontal distance covered by the target during said interval can be measured and the corre- 10 sponding speed determined. For example, if S is the distance in feet represented by 1" on the plotting surface, and d is the distance measured in inches and covered by the target during a predetermined interval of t seconds, then the horizontal velocity of the target expressed in miles per hour. Thus where 1"= mile or 660' to the scale of the chart, and a time interval of 10 seconds is selected, if the distance measured upon the chart between two instantaneous target positions, is 6 inches, then the horizontal speed of the target is known to be approximately 270 miles per hour. Thus it becomes possible to graduate scale 3| to read directly in mile per hour target speed and to read such speed directly from the plotter. By providing a series of scales for different time intervals, the battery commander may select in advance, the interval found most desirable for the particular situation. Figure 16 shows a scale graduated in miles per hour for an interval of ten seconds. Preferably transmitter I8 is connected so that it transmits the angle between scale 3| and slot I4, which angle is equal to the angle between the normal to the target course and base line 22.

Arm 24 is graduated to read in feet or yards, as desired, and to the scale of the plotting mechanism, and is used to read off directly the distance E, previously described.

Thus, a target is selected and sighted at stations 0! and O2, arms 29 and 38 are correspondingly moved. At any given time the operator plots the point of intersection of the radial edges of said arms, starts his stop watch and, at the end of the predetermined interval, again plots the intersection of said arms. Scale 3! is immediately moved to align with the two points thus plotted. Since scale Si is slidable within the channel of guide element 20, it may be moved to bring one end in coincidence with one of the points located while the speed of the target is read off directly on the scale opposite the other point. If desired, to facilitate this procedure, the scale may have two sets of graduations running in opposite directions from a zero mark at the respective ends.

Arm 24 is next rotated until it is perpendicular to scale 3| and the distance E is noted and transmitted to the computers. The battery commander then selects the number of the firing point to be used and communicates the number to the operators at the train and elevation computers.

The train angle computer At Figures 10 and 11, I have shown one form that the computer l5, used in my invention, may take. A casing 32 of generally cylindrical shape may be supported upon tripod legs 33. Casing 32 has its top edge provided with a scale of angular degrees 34 and, radially projecting from one side wall, a hollow boss 35, adapted to rotatably support a shaft 36 of an electric telemetric repeater 31, whose casing is adjustably secured to boss 35. Shaft 36 has a pinion 38 fixed to its radially inward end. Casing 32 also has a central upstanding boss 39, counterbored to receive an anti-friction bearing 40, held in place by a collar 4!.

A circular chart plate 42 has a central boss 43 which fits the inner race of bearing 63, whereby the plate A2 is mounted for rotation about a cen' tral vertical axis. A crown gear 44 on the under side of plate 42, meshes with pinion 38 so 1 1 that the plate is automatically rotated by operation of repeater 31. Plate 42 is adapted to receiveand support a pre-computed chart, formed in a manner subsequently explained.

A second circular boss 45 is located on casing 32 within and concentric of boss 39 and is counterbored to receive spaced vertically-aligned anti-friction bearings 46 and 41. These bearings support a central shaft 53 for rotation about the central vertical axis of plate 42. At its top end, shaft 53 carries a hub 48 that, as shown at Figure 11, may have a central aperture and communicating key Way 49 formed axially therein and in which, a correspondingly shaped projection 50 is adapted to fit when hubs 48 and are brought into one, and only one angular relation.

'Hub 5| has secured thereto an arm 51, preferably of transparent material. This arm.eXtends radially of the axis of shaft 53 and is made of length such that a pointer 52 of a slide 58 may be moved therealong to any position on a chart upon plate 42. The pointed end of arm 51 moves in indicating relation over and about the scale on rim 34.

A bevel pinion BI is secured to the lower end of shaft 53 and meshes with a bevel pinion 54, fixed to one end of a shaft 55. A sub-casing B0, is secured to the under side of casing 32, as by bolts 56. Aligned anti-friction bearings 53 and 64 are mounted within integral portions of subcasing 60 and'rotatably support shaft 55. One end of shaft 55 projects to the exterior of casing 60 and there carries a hand wheel 59. A bevel pinion 62 is secured to shaft 55. Casing 60 has a transmitter 65 fixed thereto, having its rotor shaft 66 connected to be driven by shaft 55 through bevel gears 62 and 61. Thus as hand wheel 59 is turned, arm 51 is rotated over plate 42 and the rotor of transmitter 65 is turned a proportional amount whereby to transmit said rotation to the gun and to the elevation computer, as subsequently explained. It will be understood, of course, that the transmitter 65 may be replaced by a flexible shaft drive, to control the actuation of the parts at the gun since the two will ordinarily be positioned near each other.

As the gun train angle is measured with respect to a fixed base line such as B, while the target path may have any angular relation to the aforesaid base line, it is desirable that the angular values involved be accurately represented so that the correct azimuth angle of the selected aiming point may be instantly and continuously indicated. This is the function of the train angle computer in connection with the computing chart, presently described.

The gun train angle computing chart The gun train angle computing chart I00, is shown at Figure 12 and may be laid out and constructed as follows. A diameter X-X is drawn and a central point G is located thereon to represent the gun position. Points are then located on the diameter at a distance from G proportional to certain assumed E1 or target plane distances as, for example, 500, 1000, 1500, 2000 and 2500 yards. With point G as a center, semicircles are drawn on the diameter, through the points thus determined and construction perpendiculars to diameter XX are drawn at the points where these semi-circles intersect the diameter, including a perpendicular through point G. These perpendiculars represent the traces, on a horizontal plane through the gun position, of vertical planes through the respective firing points such as TI, T2, etc., normal to the line XX, and the lines are so labeled for identification. Now to construct a curve for firing points T3, for example, a radius is located through G and the point where the 500 yard firing plane intersects the T3.plane. The point where this radius intersects the 500 yard circle is noted and plotted. Next, a radius is passed through G and the point where the 1000 yard firing plane intersects the T3 plane. The point where this radius intersects the 1000 yard circle is plotted. Similar radii are located for the T3 plane at the 1500, 2000 and 2500 yard circles and the points where'each radius crosses its corresponding circle is plotted. As many points as are needed are thus located, and a fair curve is drawn through them, thus determining the T3 curve shown. Curves Tl, T2, T4, etc., are determined in a similar manner.

Thus, if it be assumed that a chart constructed as just described, has been applied to plate 42 and so oriented that base diameter XX' is parallel to the target course L, Figures 1 and 3, while slide 58 has been moved radially until its pointer 52 indicates the previously determined target plane or E distance, then rotation of said arm until pointer 52 intersects the curve corresponding to the firing point selected, will locate said arm so that the radial line thereon, lies in a vertical plane passing through the represented gun position and the selected firing point. In short, if the instrument of Figure 10 has been set up so that the 0-180 line on rim scale 34, is parallel to base line OIG, and plate 42 has been 'rotated relatively thereto by repeater 3'! so that the chart diameter is parallel to the target course, then rotation of arm 51 as aforesaid will cause its indicating line to indicate upon scale 34 the correct angle of train of the guns relatively to the base line 0 l-G for the firing point selected.

It has been assumed for simplicity of explanation that the various lines on instrument l5, Figure 10, are moved into parallelism with the actual lines in space that they represent. However, it Will be appreciated that this is not necessary and that, so long as the instruments are properly calibrated, connected, and initially adjusted, that the angle indicated by arm 51 upon scale 34, will give the correct train angle for the guns for the firing point selected no matter what its position may be relatively to the horizontal or vertical planes.

Furthermore, since changes of elevation of the selected firing point do not affect the train angle thereof, only one such chart is required for all 7 conditions of fire.

Thus, the actual train angle to be used, is proportional to the rotation of hand wheel 59, and such rotation may be used either to train the gun directly or through any well known power followeup or follow the pointer system.

The gun elevation angle computer For any given E distance, that is, the minimum distance from the gun, of the vertical plane through the target path, the angle of site of the gun required to aim at any selected point, will vary with the elevation of that point above the horizontal datum plane through the gun position. At midpoint of the target path, that is, when the target is at point T5, Figure l, in a target plane having any E distance, the angle of the site of the gun will be the dihedral angle between the aforesaid horizontal datum plane and the slant plane through the gun position and target path. For other firin points, the angle of site of points in that path will decrease upon both sides of the midpoint. In other words, for any given horizontal target path, the angle of site of the gun in tracking the target, will increase to a maximum at midpoint and then decrease. Consequently having determined the gun-target path slant plane it becomes necessary to determine the angle of site (the angle 0, Figure 1) necessary to cause the bore axis of the gun to pass through the selected firing point. The angle of superelevation it is then added to give the quadrant angle of gun elevation.

The correct angle of site is computed by the instrument I1, shown at Figure 3 in the general system and in detail at Figures 13 and 14. A base plate IOI is provided with three legs, I02, each having a leveling screw I03 by which the instrument may be supported on an substantially horizontal support. Plate MI is conveniently circular and has a central upstanding boss or wall I04 and a downwardly-flanged opening I05, to receive and mount a telemetric repeater I05. A support I01 has a central cylindrical flange I08 fitting boss I and rotatably mounting the support I01 upon plate IOI. A nut I09 engages the projecting threaded end of boss I04 to prevent separation of support I01 from plate MI. The support has a depending rim portion I I0 adapted to be received by guides III secured at spaced intervals about the periphery of base plate IOI to afford a support for rim I I0. One of these guides is formed as a pair of jaws H2 and H3, Figure 14, adapted to be drawn together by a clamping screw II4 threadedly engaging jaw II3 to clamp rim I I0 and thereby lock support I01 to plate IOI A pair of diametrically opposite standards H5 and H0 are bolted to support I01 and have aligned bearing apertures together defining a horizontal axis I I1 parallel to support I01 and concurrent with the vertical axis H8 defined by boss I04. A bail H9 conveniently of generally rectangular shape has its ends bent outwardly for reception in the apertures of standards 5 and I I6 whereby the bail is mounted for pivotal movement about axis -I I1 and, of course, moves with support II]? as the latter rotates about axis H0. At its left side, as seen in Figures 13 and 14, the bail carries an elbow telescope or sight I20, of conventional construction, having an eyepiece HI and an objective I22. The axis of eyepiece I2I is convenientl aligned with axis I I1 and may have an aperture in a lug I23, receiving the adjacent projecting end of bail II9. A clamp- I 24 fixes the barrel of telescope I20 to bail H9 in position such that the optical axis of the telescope is normal to axis III for all rotational positions of the bail and telescope. The bail is provided at its central portion with a bearing block I25 rigidly fixed thereto and defining an axis I21 parallel to the optical axis of telescope I20, concurrent with axes II! and H8 at point I26, and normal to axis II1.

A stub shaft I 28 is journaled within boss I04 and has a flange I29 resting upon the top thereof. At its projecting end beneath plate I0 I, shaft I 28 carries a gear I30 in mesh with a worm I3I fixed to the armature shaft of repeater I05. The upper end of shaft I 2-8 has fixed thereto a yoke I32 having upstanding apertured lugs I33 and I34 at its ends. The apertures in these lugs are aligned to define an axis I31, which, in the position of the parts shown, is coincident with axis I I1. It is desired to emphasize, however, that the axes H1 and I 31 may have any angular relation in a plane parallel to support I01. A shaft I35 is journaled in the atoresaid apertures. A scale plate I36 ex- 14 tends through an arc of a little more than and is attached to the ends of shaft I35. This scale carries curves of gun elevation, constructed in a manner to be subsequently explained.

A slide or frame I38 has spaced arms I39 and I40 whose side surfaces define a plane I42, and a shaft I4I journaled in bearing block I25. The axis of this shaft also lies in the aforesaid plane, as will be noted from Figure 17. A transparent pane I43 fits between and is secured to, the rabbetted inner edges of arms I39 and I40 and has a reading line I44 extending along axis I21 which also, in the position of the parts shown, forms a radius of arcuate plate I36. In the species shown, there is no mechanical connection between slide I38 and plate I 36 so that the latter, for example, might be turned downwardly from the position shown in Figure 13. It is contemplated, however, that the two might be interconnected as by having a second pair of arms such as I39, I40, on the under side of slide I38, and forming guideways through which plate I36 may slide. Since slide I38 is p-ivotable about the axis I31 of shaft I4 I, it may be brought to lie flat against scale I36 for any and all angular relations of axes II1 and I31. A set screw I45 is threaded into an aperture in lug I33 and may be turned down to engage shaft I35 and thus lock scale I35 in any desired position of adjustment about axis I31.

A protractor scale I43 is fixed on standard 'IIS concentric of axis II1. A Vernier I41" is mounted upon the adjacent side portion of bail H9, and moves along the graduated edge of protractor I46 to indicate the angles of elevation above the horizontal plane, of the plane determined by bail H3 and the line of sight of telescope I 25. A transmitter I41 is carried by standard H6 and has its armature connected in any suitable manner, to be driven by angular movement of bail H9. From Figure 3 it will be noted that this transmitter is connected by way of a cable I48 with a repeater at the gun and controlling or indicating the proper elevation thereof. It will also be noted from this figure, that transmitter I 8 controls both repeater 31 of the train angle computer, as well as repeater I05 of the elevation angle computer. The connections are such that repeater I06 acts to maintain shaft I35 parallel to the target path. Since the elevation angle computer depends for one input upon direct sighting, it will be clear that the axis of shaft I35 must be parallel to the actual target course.

As shown upon Figure 13, the rim IIO of support I 01 may have a scale thereon cooperating with an indicator such as I49, Figure 13, to denote the angular relation between the two. In fact, by providing suitable means transmitting the angular relation of support I01 relatively to base plate HM, and positioning the scale on rim Hi0 :s-uch that indicator I49 will be at zero when shaft I35 is parallel to base line B, it is possible to use instrument I1 to determine the gun train angle for any selected aiming point. In such cases, instrument I5 might be dispensed with, although I now prefer the arrangement shown.

The can elevation and .superelevatioat computing charts The scale upon plate I36 is formed by first drawing thereon a plurality of spaced concentric arcs about the center of plate I30. In Figures 13 and 14, and in agreement with the chart of locked in position by tightening screw I45.

Figure 12, I have shown four arcs, equally spaced from the outer edge of the scale and corresponding to target plane distances, reading outwardly of 500, 1000, 1500, 2000 and 2500 yards, the outer edge of the scale itself serving as the 2500 yard line. Considering the axis II8, as shown upon Figure 14 as the T or control firing plane and its intersection with axis I31 as the origin corresponding to point I26, Figure 14, lines equally spaced and parallel to axis II8, are drawn from axis I31 as a base line and labeled from right to left T0, TI, T2, to T9. Next, a series of five equally-spaced lines are drawn parallel to axis I31 and labeled 500, 1000, 1500,etc. Now, to construct a curve corresponding to the T3 firing plane, that is the vertical plane containing all T3 firing points, a radius is drawn through point I26 and the point where the T3 plane intersects the 500 yard firing plane. The point where this radius intersects the 500-yard are on scale I36 is plotted. Next, a radius is located through point I50 and the intersection of the T3 plane with the 1000-yard firing plane. The point where this radius crosses'the 1000-yard arc is plotted. Similarly, points are located upon each of the remaining arcuate lines upon scale I36, and a fair curve drawn through the points thus located and labeled T3. Similar curves are determined in a like manner for each of the other firing planes. It will be understood, of course, that the number of firing planes and target range planes used in the construction of the curves should be the same as used in construction of chart I00, Figure 12. However, the number of planes selected for construction of the two charts and the ranges covered thereby, will depend upon experience and the effective range of the gun for which they are prepared.

The operation of the elevation computer I1 will now be explained. The instrument is set up and leveled by means of screws I03. The telemetric connections are made over cables I5I and I52, Figure 3, from transmitter I8 so that repeater I06 acts to maintain shaft I35 parallel to arm 3I of the plotter II. Before a computation, scale I35 may be folded down into a position substantially parallel to support I01. The operator now uses telescope I20 to sight upon the target and in so doing, rotates support I01, while rotating bail I I9 about its axis II1. Thereby, he determines a line of sight from the gun position to the target; and shaft MI is at all times parallel t this axis. Since shaft I35 is parallel to the target path, and axis I21 of shaft I4I lies in the target plane, there are materialized two intersecting lines, both lying in the slant plane determined by the gun and target path. Scale I36 is now rotated about axis I31 until it engages the under surfaces of arms I39 and I40. When this is done, scale I36 is known to lie in the aforesaid slant plane and is The number of the firing point selected, as well as the distance E of the target plane are known. Hence the operator now rotates support I01 until the reading line I44 passes through the point determined by the curve corresponding to the selected firing point and the' known E distance. In so doing, the slide I30 moves over and in contact with scale I36 and the elevation of bail I I9 is altered. When the correct adjustment has been made, the angle of site of the gun for the firing point selected, will be indicated on scale I46 by vernier I41 and is, of course, transmitted to the gun by transmitter I41.

If desired, protractor I46 and vernier indicator I41 may be replaced by the superelevation computer of Figure 15. In this figure, II9 represents a portion of the bail as in Figures 13 and 14, having a transparent indicator plate I53 secured thereto. A reading line I54 is formed on this plate, extending radially of a quadrantal plate I55 fixedly mounted upon standard H6, in substitution for protractor scale I46. This plate bears a series of equally spaced arcs I56 concentrio of axis II1 of bail H9, and representing ranges of 0, 500, 1000, 1500 yards, etc. as indicated on the chart. As is Well known, the superelevation correction is a function of the cosine of the angle of gun elevation and range. The curves are therefore arranged to indicate increased elevation radially inwardly, in accordance with range, the increase varying from zero at indicated elevation, to a maximum at 0 or point blank elevation, in accordance with the cosine function aforesaid. Various charts may be prepared for each type of ammunition used with the gun, each based upon the average velocity of the projectile for the respective types of ammunition. In use, the angle of site is indicated at the periphery of plate I55, exactly as in the case of protractor I46. The bail H9 is then given an additional elevation until the reading line I54 intersects the point on the curve corresponding to the known range of the selected firing point. For example if, in a given situation line I 54 coincides with the 35 curve at the edge of plate I55, while the range of the selected firing point is 2000 yards, bail H9 is elevated untilline I54 passes through the intersection of the 35 curve with the 2000 yard arc. This motion is, of course, transmitted to the gun and used to give the latter the proper angle of quadrant elevation.

The Lead Angle The lead angle is introduced by rotating the sight upon the gun, in the target slant plane. It has been explained that this angle is the angle subtended at the gun, by a distance equal to the product of target speed and time of flight of the projectile which product is obtained from values set up on the plotting instrument. The value obtained from the plotting board will be the angle a which, as has been explained is the projection of the slant plane lead angle a: upon the horizontal plane. Since the slant plane is determined by scale I36, the true lead angle may be set off merely by rotating support I01 relatively to base plate IOI through the angle 6 and noting the corresponding angle to of movement of slide I36 relatively to plate I36. For this purpose, a scale of angles may be provided about the inner periphery of plate I36 as shown at Figure 14. The sight is then set off relatively to the gun in the slant plane and the gun is fired when the target is seen along the line of sight.

Actually in accordance with the foregoing procedure, the sight I20 is first directed upon the target, then moved so that its line passes through the selected aiming point, then returned in the direction of the target by the slant plane lead angle. Hence the sight I20 is itself directed upon the point at which the target will be located when the-gun is fired. Since instrument I1 will be located in proximity to the gun, so that parallax will be negligible, the sight I20 may itself be used to determine the instant of firing. Such use of instrument I1 is contemplated and is within the purview of the invention. The sight at the gun itself is not shown but may comprise any standard elbow telescope such as the Army's M6 or l7 M6Al, mounted to elevate with the gun but disconnectable therefrom as the gun is moved through the angle of superelevation. The sight is also pivoted upon an axis lying in a normally vertical plane and perpendicular to the line of sight. Thus, during the elevation of the gun through the angle of site, the telescope elevates as a un 31". ewith. At a given signal, the sight is discbunected from the gun while the latter is adjusted through the angle of supcrelevation. Finally, the sight is pivoted about the aforesaid axis through the slant plane lead angle. It is contemplated that this final lead angle adjustment or the sight may be automatically effected by a telemetric repeater connected to drive the sight, controlled by a manually-actuated transmitter at the instrument ll. This drive, of course. may he mechanical where the instrument ii is located closely adjacent the gun.

Operation scale all longitudinally to bring the li ament with the edge of arm 24. plot 1' is performing the operations, the commander notes the tactical situae. g., present location, and apparent objective of target, and selects an aiming point from 3i and communicates the same to the plotter as well as the operators at instruments l5 ii. The plotter now turns scale 2 until its edge passes *hrough the selected aiming point as ted on scale 3i and reads off the range thereof on scale fit. Having done this, his Work for that firing point is completed and he may turn his attention to plotting new points from the intersections of arms 29 and Eli in preparation for a new firing point. The battery commander announces the firing point and computes the lead angle from the now known target speed and of fiight of the projectile.

i8 to transmit the angular movement .cf to efiect operation of repeaters 3? and at the instruments l5 and ii, respectively. rotates plate 42 and the chart iilll thereon, through the angle between lines 13 and L, Figure so that base line X..', Figure 12, is, to simpl fy the explanation, parallel to line L. The operator at instrument it moves slide 58 outwardly until its pointer 52 indicates the determined E distance on arm 5?, then rotates hand wheel 59 until the pointer is over the curve corresponding to the selected firing point. This operation actuates transmitter and transmits the correct train; angle to the gun where, as previously expla d it is used to automatically train the gun or to indicate the proper train angle so that the:

gun may be manually controlled for rotation through the indicated angle.

At instrument ll, repeater IE6 turns shaft I35 into parallelism with scale Bl, Figure 7. The op- 5 erat or then sights the target through telescope I26 by combin d rotation of support iii? and hail I 19. He then rotates plate I36 into contact with slide E38, locks shaft 535 by screw and by a combined turning of support NW and rotation of 10 bail H9, brings reading line E l s to the intersection of the curve corresponding to the selected firing point with the arc corresponding to the determined target plane or E distance. In so doing, bail 5 i9 is moved angularly about its axis ill to the correct angle of site, which is transmitted by way of transmitter It? to the gun where it may be used automatically to elevate the gun by means of a known servomotor system, or to merely indicate the correct elevation under manual control. The sight at the gun, if used, is then disconnected from elevation with the gun, and the gun is additionally elevated for superelevation as previously described in connection with Figure 15 While leaving the sight in its pre- 5 viously effected angle of site adjustment. The support till is then moved through the angle 6 as determined by the plotter, and the corresponding angle or is noted on scale I36 and applied to the sight. The gun is then fired when the target 0 appears at the intersection of the cross hairs of the telescope. The entire procedure thus described is performed smoothly and numerous steps are performed simultaneously. Hence the total time required is but a few seconds from the 5 time the target is first tracked at stations 01 and 02, until the gun is fired. Moreover, as the various steps are completed, the operating personnel may immediately begin the observations and computations for a succeeding firing point, thus reduc- 40 ing the time between bursts to a minimum.

The system has been disclosed with the firing points increasing in number from right to left. In such cases, where only One scale of firing points is used, the battery commander will of course, select a point of lower number, when the target is proceeding from left to right. In lieu of that, it is contemplated that two scales may be used, preferably in different colors. Thus chart Figure 12, might have a first scale as shown and a second scale with present points T9, T8, etc., identified as Tl, T2, etc., respectively. Furthermore, to avoid confusion it has been assumed that the target course lies to one side only of the system. The system is not so limited but may easily be adapted for use throughout 360 of azimuth. Thus, plotter C may be enlarged to include a full 369 circle of azimuth, and With transmitter is and scale 3! translatable along a full dia iieter of the circle. By making certain 50 that the ordinals of the firing points, as designated upon scale 3i, always increase for a target traveling left to right instruments i5 and El may be used without change, it being understood that scale extends through 360 of azimuth.

it is contemplated that a standard iuze setter will be located adjacent the gun and will be set from a control means adjacent instr nicnts i5 and il in accordance with the known range to the selected aiming point. Also, when desired, the tpeateis herein disclosed as directly actuating the sight or sights at the gun, may he positioned in a control box as described in subsequently-identified application. The sights at the gun or guns may then be manually actuated under control of a match-the-pointers arrangement of the control box. Such an arrangement is especially desirable where a battery of guns are controlled from a single system and it is desired to efiect a slight dispersement of the bursts of the several guns to thereby increase the probability of a hit. This function may be effected by slightly varying the train and elevation angles used to set the sights of the respective guns.

The system herein disclosed is adaptable for all types and sizes of mounted guns. The number of firing points and their spacing, as well as the extent of ranges selected may be varied at will for best results with the gun and ammunition used. It should also be noted that interpalation is easily efiected in the adjustment of all component parts of the system so that all adjustments may be made on the basis of the exact minimum range as determined by plotting instrument II. The system disclosed is relatively simple and will be found particularly effective when used in connection with ammunition using VT or proximity fuzes.

While I have shown the preferred form of the invention as now known tome, it will be obvious to persons skilled in this art that numerous modifications and substitutions in addition to those suggested, may be made without altering the basic principles upon which the invention is founded. For example, it has previously been shown how the function effected by instrument I may be taken over and performed by instrument ll where rapidity of computation is not essential as, for example, in firing at slow-moving aerial or surface targets. It has also been explained how sight [26 may itself be used to determine the instant of firing of the gun, where such sight is positioned adjacent the gun so that parallax is negligible. Numerous other modifications Will be obvious or occur to those skilled in the art of gun fire control after a study of the present disclosure; and it is my desire and intention to reserve all such changes as fall within the scope of the subjoined claims.

This application is a continuation in part of my abandoned application, Serial Number 328,- 506, filed April 8, 1940, for Fire Control System.

Having now fully disclosed m invention, what I claim and desire to secure by Letters Patent is:

1. For use in a gun fire control system, a plotter comprising a supporting surface, a pair of arms pivoted on said surface at spaced first and second points, a third gun-position point on said surface, all said points representing to scale the actual spatial relation of a gun and two observation points spaced from said gun and from each other, said third point and one of said first or second points determining a base line, a transmitter including a stator and a rotor, means mounting said transmitter on said surface for rectilinear movement in a path normal to said base line through said third point, and a scale extending radially of said rotor and pivotable as a unit therewith.

2. A plotter as specified in claim 1, said scale being longitudinally adjustable with respect to the pivot axis of said rotor and having a scale of target speeds thereon based upon a known time interval between points successively located by intersection of said arms.

3. For use in a gun fire control system, in combination, a base, a pair of arms pivoted on said base at respective, spaced, first and second points, each representing a corresponding observation station, a third arm pivoted on said base at a third point representing a gun position, all said points being positioned to scale in the spatial relation of the actual observation stations and gun position, a universally pivotable sight at each said observation point, telemetric means synchronously rotating each of said pair of arms by and in response to the horizontal component of movement of a respective sight, said third point and one of said first and second points, determining a base line, there being a slot in said base extending radially from said third point normal to said base line, a slide guided for translation by and along said slot, a transmitter carried by said slide, said transmitter having an armature shaft, a channeled guide element fixed to said shaft, and a speed scale in the channel of said element for longitudinal translation only, radially of said shaft.

4. In a plotting instrument for gun fire control, a base plate, first and second arms pivoted on said plate at respective first and second spaced points thereon representing observation stations, a third arm pivoted upon said plate at a. third point representing a gun position, said third point and one of said first or second points determining a base line, a telemetric transmitter, means mounting said transmitter on said base for translation only radially of said third point, said transmitter including a rotor shaft, a slide carried by said shaft, and a fourth arm guided for longitudinal sliding by and along said slide, said fourth arm having a. target speed scale thereon, all said arms being rotatable in respective, spaced planes parallel to said base plate.

5. The plotting instrument recited in claim 4, and telemetric repeaters carried by said base plate, each being connected to rotate a respective one of said first and second arms in response to the component rotation of a respective one of a pair of remote observation instruments.

6. In a gun fire control system, a gun located at a first point, a pair of observation instruments located at second and third points spaced from each other and from said first point, a plotter having first, second and third arms pivoted at points representing to a reduced scale, the spatial relation of said first, second and third points, respectively, transmitter means operated by and in response to movement of said observation instruments in tracking a target, to rotate said second and third arms, respectively, a transmitter, means mounting said transmitter on said plotter for translation thereover, a speed arm translatable with said transmitter and rotatable into alignment with two points on said plotter located by successive points of intersection of said second and third arms, a gun train angle computer, a gun elevation angle computer, and first and second repeater means on said computers, respectively, connected to be actuated by and in proportion to the rotation only of said transmitter by said speed arm.

7. In a gun fire control system a gun located at a first point, a pair of observation instruments located at second and third points respectively and spaced from each other and from said first point, a plotter having first, second and third arms pivoted at points representing to reduced scale, the spatial relation of said first, second and third points, respectively, transmitter means operated by and in response to movement of said observation instruments in tracking a target, to rotate said second and third arms, respectively, a first transmitter, means mounting said transmitter on said plotter for translation thereover, a speed arm translatable with said transmitter and rotatable in alignment with two points on said plotter located by successive points of intersection of said second and third arms to correspondingly actuate said transmitter, a gun train angle computer comprising a casing, a chart plate pivoted on said casing for rotation upon an axis normal to said plate, a radial arm pivoted on said casing for rotation about said axis and over said plate, a slide on said arm movable radially of said axis in accordance with a chart on said 10 plate, first means operable to rotate said arm over said plate, a second transmitter carried by said casing and driven by said first means, a repeater carried by said casing and operable to rotate said chart plate, driving connections between said first transmitter and repeater, a gun elevation angle computer, comprising a base, a support pivoted on said base for rotation on a first axis relatively thereto, a bail pivoted on said support on a second axis normal to said first axis, a sight connected for movement with said bail and determining a line normal to and intersecting said second axis, a shaft j ournaled on said base on said first axis and defining a third axis coplanar with said second axis, an arcuate scale plate carried by said shaft and having said third axis as a diameter, a frame pivoted on said bail on a fourth axis normal to said second axis and adapted to engage said scale plate when said fourth axis and scale plate are coplanar, all said axes being concurrent at a single point, a second repeater mounted on said base and connected to 22 rotate said ball, and driving connections between said second transmitter and said second repeater.

JQHN E. REIERSON.

REFERENCES CITED The following references are of record in the file of this patent:

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